DE60029538T2 - Method for producing a helical antenna of four conductors and antenna produced by this method - Google Patents

Description

These The invention relates to a method for producing an antenna, mainly to a method of tuning a four-wire helical antenna for circular polarized radiation at frequencies above 200 MHz. The invention also includes an antenna made by the method.

The Four-wire backfire antenna is well known and is becoming particular when transmitting and receiving circularly polarized signals or applied by orbiting satellites. GB 2292638-A discloses a miniature four-wire antenna with four helical antenna elements of half wavelength in the form of narrow, clad on the surface of a cylindrical ceramic core conductive Strips. Radial connecting elements on the distal end face of the Kerns connect the helical Elements with a coaxial feed line, in a narrow passage axially through the core. The helical ones Elements are arranged in pairs, with the elements of a pair a larger electrical Length as those of the other pair have, following a meandering course and all four elements connected to the edge of a conductive balun sleeve are one lying in a plane perpendicular to the antenna axis Circle describes. GB-2310543-A discloses an alternative antenna at the balun pod has a non-planar edge, the helical elements simple screws are in peaks or valleys of the border, so that elements of different lengths result.

The Fact that the element pairs have different electrical lengths, leads to a phase difference between the currents in the respective pairs at the operating frequency of the antenna, and this phase difference makes the antenna sensitive to circularly polarized radiation having a cardioid directional characteristic, allowing the antenna to receive circularly polarized signals from sources directly above the antenna, d. H. in the antenna axis, or in few positions Degrees above a perpendicular to the antenna axis aligned and this interspersed Plane or from sources somewhere in the solid angle between these extremes suitable is. The directional characteristic is also due to an axial Zero point marked in the opposite direction to the direction of maximum profit.

The Bandwidth of the four-wire resonance described above is relative narrow, and prepares, especially for miniature four-wire antennas with a core high dielectric constant, a manufacturing problem in meeting sufficiently tight dimensional tolerances for the reproducible production of antennas with the Kardioidverhalten and the resonance frequency as required.

To A first aspect of the invention is a method for Production of a four-wire antenna for circularly polarized radiation at frequencies above 200 MHz, which is a plurality of essentially helical Abstrahlbahnen arranged on a dielectric substrate are, with the procedure monitoring of at least one electrical parameter of the antenna and the Remove conductive Material from at least one of the webs comprises the inductance of the web to increase and thereby the supervised Parameters closer to bring to a predetermined value. So can the circularly polarized Directional characteristic of the antenna can be improved. One can also Trim antennas in mass production, without having to go through individual tests, for example, in an electromagnetically echolous chamber, and excessive manual Intervention.

The preferred methods include removing the conductive material from the tracks by laser etching an opening in one or more of the tracks, the opposite edges of the affected lanes remain intact on both sides of each opening. This Method is particularly applicable to an antenna in which the substrate a substantially cylindrical body of ceramic material with a dielectric constant greater than 10, the webs sections on a cylindrical surface of the Substrate and additionally on a flat face, which is substantially perpendicular to the cylinder axis include. In this case, the conductive becomes Material from the track sections on the flat face, the in the preferred antenna near the feed point of the antenna elements lies and a point of a voltage minimum in four-wire resonance is removed. In alternative embodiments, the opening (s) may be cut at locations other voltage minima, for example where the helical Elements on a common connection conductor as one the core surrounding balun sleeve to meet.

The monitoring step typically involves connecting the antenna to a radio frequency source, which is arranged to have a frequency containing the operating frequency Frequency band sweeps over, and monitoring the relative phases and amplitudes of signals generated by probes in juxtaposition with the tracks at predetermined locations, as the end portions remote from the feed point become. Preferably, the probes are capacitive with the corresponding traces coupled to make an individual ground connection unnecessary.

The in the tracks shaped openings are preferably rectangular, each having a predetermined width across to the train direction, which automatically in response to the result of the monitoring step is calculated. This is a non-linear adjustment process, as that added through the opening inductance the web is non-linear with the opening area, in particular with the width of the rectangular opening, is related. The Calculation of the opening size is so performed that the phase difference of the currents and / or stresses in the tracks of the respective pair of tracks closer to 90 ° and the Frequency at which this orthogonality occurs, closer to the intended operating frequency.

To In a second embodiment, the invention also includes a four-wire antenna for circularly polarized Radiation at frequencies above 200 MHz with several substantially helical conductive tracks on a dielectric substrate, wherein at least one of the tracks a section of predetermined size for increasing the inductance of the web having. The preferred antenna has a substrate with one out an antenna core formed of a solid dielectric material, wherein the webs are arranged to define an internal volume, whose main part is occupied by the solid material of the core, and wherein the substrate is curved Outer surface portions and level, the conductive Web-bearing surface sections and wherein each cutout is formed where the corresponding one Train over one of the flat surface sections lies.

The Invention will now be described by way of example with reference to the drawings, in which in which

1 is a perspective view of a dielectrically loaded four-wire antenna,

2A and 2 B Top views of the antenna behind 1 before and after adaptation according to the invention,

3 is a diagram which the conductor pattern on the cylindrical surface of the antenna according to 1 shows,

4 is a graph showing the changes of phase and amplitude with the frequency of signals measured at different points of the antenna,

5 is a diagram showing a test arrangement for use in a manufacturing method according to the invention, and

6 a cross section through one of in 5 is visible probes.

The The four-wire antenna described below is similar to that in the aforementioned GB-2310543-A the disclosure of which is hereby incorporated by reference Description is included. Also the revelation of the above Related GB-2292638-A is incorporated by reference into this specification added.

Regarding 1 . 2A . 2 B and 3 For example, an antenna to which the present invention is applicable has an antenna element structure having four longitudinally extending antenna elements 10A . 10B . 10C and 10D acting as narrow metallic conductor sections on the cylindrical outer surface of the ceramic core 12 are formed. The core has an axial passage 14 , which is a coaxial feed line with an outer shield 16 and an inner conductor 18 houses. inner conductor 18 and shielding 16 form a feed structure for connecting a feed line to the antenna elements 10A - 10D , The antenna element structure also includes corresponding radial antenna elements 10AR . 10BR . 10CR and 10DR acting as metallic track sections on the distal end face 12D of the core 12 are formed and the ends of the respective longitudinally extending elements 10A . 10B . 10C and 10D connect to the feed structure. The other ends of the antenna elements 10A - 10D are to a virtual ground leader 20 in the form of the proximal end portion of the core 12 surrounding cladded sleeve connected. This sleeve 20 is in turn by a plating on the proximal end face 12P of the core 12 to the shield 16 the food structure 14 connected.

The four longitudinally extending elements 10A - 10D have different lengths, with two elements 10B and 10D longer than the other two 10A and 10C are because they are closer to the proximal end of the nucleus 12 extend. The elements of each pair 10A . 10C and 10B . 10D are diametrically opposite on opposite sides of the core axis.

For an approximately uniform radiation resistance for the helical elements 10A - 10D To maintain, each element follows a simple helix. The upper connecting edge 20U the sleeve 20 has changing height (ie changing distance from the proximal end face 12P ) to provide connection points for the short or long elements. Therefore, in this embodiment, the connecting edge follows 20U a zig-zag way around the core 12 with two peaks and two valleys, where he with the short elements 10A . 10C or the long elements 10B . 10D coincides. The amplitude of the zigzag path is in 3 denoted by a.

Each pair of helical and corresponding connecting radial element sections (e.g. 10A . 10AR ) forms a conductor with a predetermined electrical length. Each of the element pairs 10A . 10AR ; 10C . 10CR with the shorter length produces a shorter transmission of about 135 ° at the operating wavelength than each of the pairs of elements 10B . 10BR ; 10D . 10DR , The average cycle time is 180 °, equivalent to an electrical length of λ / 2 at the operating wavelength. The different lengths create the necessary phase shift state for a four-wire helical antenna for circularly polarized signals as specified in Kilgus, "Resonant Quadrifilar Helix Design", The Microwave Journal, December 1970, pages 49-54. Two of the element pairs 10C . 10CR ; 10D . 10DR (ie a long and a short pair of elements) are with the inner ends of the radial elements 10CR . 10DR to the Innenlei ter 18 the food structure at the distal end of the core 12 connected while the radial elements of the other two pairs of elements 10A . 10AR ; 10B . 10BR with the through the outer shield 16 formed dining shield are connected. At the distal end of the feed structure are those on the inner conductor 18 and at the food shield 16 existing signals are approximately symmetrical so that the antenna elements are connected to an approximately symmetrical source or load, as will be explained below. It is recognized that in general that of the web sections 10A - 10D and 10ar - 10DR formed webs have an average electrical length of nλ / 2, where n is an integer, and n / 2 turns around the antenna axis 24 can execute.

In the left-handed direction of the screw paths of the longitudinally extending elements 10A - 10D the antenna has its highest gain for right handed circularly polarized signals.

If the antenna instead for left-handed circularly polarized signals is to be used, the screw direction vice versa and the connection pattern of the radial elements is about Turned 90 °. In the case that the antenna is left-handed for both the reception right-handed signals should be suitable which are longitudinal extending elements are arranged so that they follow paths, which are generally parallel to the axis.

The conductive sleeve 20 covers a proximal portion of the antenna core 12 and surrounds the food structure 16 . 18 , where the core material 12 the space between the sleeve 20 and the metallic lining 16 of the axial passage 14 completely filled. The sleeve 20 make one with the lining 16 through the plating 22 the proximal end surface 12P of the core 12 connected cylinders. The combination of sleeve 20 and plating 22 forms a balun, so through the food structure 16 . 18 signals formed in the transmission line between an asymmetrical state at the proximal antenna end and an approximately symmetrical state in an axial position, generally equidistant from the proximal end as the upper connecting edge 20U the sleeve 20 , being transformed. To achieve this effect, the mean sleeve length is such that in the presence of an underlying core material of relatively high dielectric constant, the balun has an average electrical length in the range of λ / 4 at the operating frequency of the antenna. Since the core material of the antenna has a shortening effect and the inner conductor 18 surrounding annulus with an insulating dielectric material 17 is filled with a relatively low dielectric constant, the feed structure has distal to the sleeve 20 a short electrical length. As a result, signals are at the distal end of the feed structure 16 . 18 at least approximately symmetrical.

The of the sleeve 20 formed wave trap provides a ring path along the connecting edge 20U for currents between the elements 10A - 10D , effectively forming two loops of different electrical length, the first with the short elements 10A . 10C and the second with the long elements 10B . 10D , In four-wire resonance exist at the ends of the elements 10A - 10D and in the connecting edge 20U Current maxima and voltage minima. The edge 20U is from the ground connector at its proximal edge through that of the sleeve 20 generated approximately quarter-wavelength wave trap effectively isolated.

The Antenna has a four-wire main resonance frequency for circular-polarized Radiation in the range of 1575 MHz, wherein the resonance frequency by the effective electrical lengths the antenna elements and to a lesser extent determined by their width is. The lengths of the elements at a given resonant frequency also hang from the dielectric constant of the core material, comparing the dimensions of the antenna substantially reduced to an air core antenna of the same construction are.

The preferred material for the core 12 is material based on zirconium-titanium. This material has a dielectric constant of over 35 and is also known for its dimensional and electrical stability at changing temperature. The dielectric loss is negligible. The core can be made by extrusion or pressing.

The antenna elements 10A - 10D . 10AR - 10DR are metallic tracks on the outer cylinder and end faces of the core 12 ge each web has a width of at least four times its thickness over its effective length. The webs can be made by plating / galvanizing the surfaces of the core 12 with a metal layer and then etching away the layer to expose the core according to a pattern applied in a photographic layer, similar to the etching of printed circuits. In all cases, the formation of the webs as a coherent layer on the outside of a dimensionally stable core leads to an antenna with dimensionally stable antenna elements. The distance between the helical track sections over the circumference is greater (preferably more than two times) than their width.

In order to obtain a directional characteristic with good front-to-back ratio and acceptable gain and to achieve this characteristic at the required operating frequency, the above-described and in 1 shown antenna subjected to a trimming process, wherein conductive material is removed from the conductive tracks to form openings, as in 2 B shown. In the connection sections 10AR . 10BR . 10CR respectively. 10DR the lanes are the openings 26A . 26B . 26C and 26D trained where there are voltage minima at the operating frequency. Since these track sections lie in one plane, it is relatively consistent to focus on the tracks at the necessary locations a laser beam to burn away the conductive material of the tracks using a YAG laser. Each opening increases the inherent inductance of the corresponding track 10A . 10AR etc. in a size dependent on the opening area. Applicants have found that the inductance added increases non-linearly with increasing extent as the width of the aperture (ie, the width of the aperture across the web) is increased. The change in additional inductance with the length of the opening (ie, along the path) is an approximately linear relationship. These relationships allow for both coarse and fine adjustments to the inductance to be made if needed.

A better understanding of the mode of operation of the antenna and the influence of the openings can be obtained with reference to the graph of 4 , 4 was observed by observing the high frequency currents in the helical track sections 10A . 10B . 10C and 10D adjacent to the edge 20U the sleeve 20 (ie the currents in the proximal end portions of the helical track sections 10A - 10D ) while receiving the antenna through its feed structure 16 . 18 was fed with a sweep signal over a frequency band comprising the required operating frequency. Four curves represent the current phase and four the current amplitude, with each current phase or amplitude curve becoming one of the track segments 10A - 10D belongs. The phase curves are indicated by the reference numerals 30A . 30B . 30C and 30D , the amplitude curves by the reference numerals 32A . 32B . 32C and 32D designated. For completeness, a ninth graph shows the insertion loss when looking at the feed structure from the source end.

The diagram 4 shows a main resonance with two coupled peaks. You can see that the amplitude curves 32A . 32C which the shorter lanes 10A . 10C have peaks on the high frequency side of the mean resonant frequency while the amplitude curves 32B . 32D Have peaks on the low frequency side. It is understood that the intersections of the four curves can be used to establish a center frequency that is in 4 through the dashed line 36 is displayed. Now you can see with regard to the four current phase curves 30A - 30D in that the curves corresponding to the tracks connected to the outer shield of the feed line 30A . 30B diverge in the resonance range. Similarly, there is a divergence between the curves 30C . 30D that with the inner conductor 18 correspond to the supply line connected tracks. The most important condition for a good front-to-back ratio in the circular polarization directional characteristic is that the phase difference between the corresponding signals in the long and short lanes should be 90 ° or an odd multiple of 90 ° (λ / 4). Therefore, regarding 4 through the phase curves 30A . 30B displayed phase values at the by the dashed line 36 designated center frequency by as much as 90 ° different, and also should by the curves 30C . 30D phase values differ by 90 °.

Of course, that should be indicated by the dashed line 36 indicated center frequency also correspond to the operating frequency of the antenna.

By adjusting the inductance of one or more of the tracks 10A . 10AR etc., one can align or trim the antenna to achieve the above-mentioned phase orthogonality and center frequency. For example, the phase divergence at the center frequency can be increased by increasing the inductance of the short paths 10A . 10AR . 10C . 10CR be reduced. The center frequency can be reduced by increasing the inductance of all four tracks. It follows that in order to fully utilize the adjustment provided by the cutting of openings, the antenna should initially be made electrically shorter than the optimum length for the required operating frequency.

These concepts can be used according to the invention as a basis for an automated antenna trimming ver be used to reduce or eliminate the deviation of the electrical parameters of the antenna (such as signal phase and amplitude in the antenna element) from the optimum values. Thus, one can produce antennas relatively cheaply using a low initial tolerance manufacturing process without resorting to costly and laborious manufacturing and adjustment procedures.

A test arrangement for performing the phase and amplitude measurements will now be described with reference to FIGS 5 and 6 described. To monitor phase and amplitude in the range of the required operating frequency, the antenna 40 in a test center in the center of a star-shaped, from the slidable on the radial rails 44A . 44B . 44C and 44D mounted probes 42A . 42B . 42C and 42D brought existing probe assembly. In the test center is the antenna 40 in the required height and angular position (made possible by a notch in one of the end faces of the antenna), so that the probes 42A to 42D on the proximal end portions 46A to 46D the tracks 10A . 10AR to 10D . 10DR aligned, ie the edge 20U the balun sleeve 20 adjacent (see 1 and 3 ). The feed structure of the antenna 40 is connected proximally to the output of a swept high frequency source in a test unit.

Regarding 6 is every probe 42 a capacitive probe with a center conductor 50 connected to the inner conductor of a coaxial cable 52 is connected, the shield is grounded to the test arrangement. The center conductor 50 protrudes from the cable 52 but is from a dielectric plastic tip 53 surrounding the end of the center conductor by a certain length (typically less than 0.5 mm), so that each probe 42A to 42D with the outer surface of the antenna 40 can be brought into contact with the top of the center conductor 50 at a certain distance to the corresponding helical path section 10A to 10D stands. Therefore, every middle conductor is 50 capacitively coupled to the associated lane and transmits signals representative of the current in the lane to the connected cable 54 and then to a corresponding fair entrance 54A . 54B . 54C and 54D the test unit (see 5 ).

You notice that in 5 two of the probes 42A . 42B in operating position in contact with the antenna 40 while the other two probes 42C . 42D are withdrawn into positions which they occupy when one antenna is replaced with another. Every probe 42A to 42D is mounted on piston to automatically move between retreat and operating position.

During the test process, all four probes 42A to 42D in contact with the antenna 40 brought, a wobbled high-frequency signal is from the output 48 the test unit 56 applied to the antenna and the at the inputs 54A to 54D received probe signals are monitored. By determining the intersections of the amplitude characteristics (as described above with respect to 4 A center frequency is calculated and then the phase values of the individual signals are read to determine their deviation from the orthogonality. From the measured values, a data record is generated, from which the required opening sizes can be calculated. A laser (not shown) then burns the openings into the exposed distal end face of the antenna as described above, whereupon another record can be generated to check that phase orthogonality and center frequency fall within the specification limits.

Actually calculated the test unit a crossover frequency, which is the closest approach which represents four amplitude curves, marks the corresponding one Frequency, reads the four phase values at this frequency for calculation the phase difference and then calculates the required for each lane additional inductance for the Shifting the crossover frequency to the required frequency (in this case the GPS frequency of 1575,5 MHz) with the correct phase orthogonality. This is done by calculation of an LC product (inductance × capacitance) for each lane executed.

Then the required opening size is calculated and the laser is for the burning of the opening (s) controlled.

Then the antenna can be automatically removed from the in 5 removed test layer and fed to a finishing process.

In order to the probes the antenna characteristics during the above described exam do not significantly affect it is preferred that the dielectric constant of the antenna core is at least 10, preferably 35 or more.

The capacitive probes pick up signals representing the extreme near field represent, and therefore can Deliver signals to the currents in the individual tracks. This allows the derivative of the far field characteristic according to the above described phase relationships.

The Removal of material is preferred with a pulsed YAG laser executed which allows the removal of metal substantially without melting, so that the dimensions are precisely controllable.

One can see the openings in the webs at other positions, such as in the proximal end portions of the web sections 10A to 10D , provided that alternative probe positions are chosen.

While the Invention concerning of a method for manufacturing a four-wire antenna was, one will understand that the procedure also on other dielectric loaded antennas, (i.e., antennas with conductors that are narrow in comparison to the distances can be applied between them).

Claims (20)

A method of producing a helical antenna for circularly polarized radiation at frequencies above 200 MHz, the antenna comprising a plurality of substantially helical conductive radiating paths ( 10A . 10AR - 10D . 10DR ), which on a dielectric substrate ( 12 The method comprises monitoring at least one electrical parameter of the antenna and increasing the removal of conductive material from at least one of the tracks by the inductance of the track, thereby bringing the monitored parameter closer to a predetermined value. The method of claim 1, wherein the conductive material is removed from the web by laser etching an opening ( 26A ; 26B ; 26C ; 26D ) in the web, the edges of the web remaining intact on each side of the opening. Method according to Claim 1 or 2 for producing an antenna in which the substrate ( 12 ) is substantially cylindrical and the webs sections ( 19A - 10D . 10AR - 10DR ) on a cylindrical surface of the substrate and on a planar surface of the substrate, wherein the conductive material of a web section or web cuts ( 10AR - 10DR ) located on the flat surface. Method according to claim 1 or 2 for producing an antenna with a plurality of helical track sections (US Pat. 10A - 10D ) disposed on a substantially cylindrical substrate surface and having a plurality of associated track connecting portions 10AR - 10DR ) disposed on a substantially planar end surface of the substrate to provide the helical track portions with an axial feed ( 14 ), wherein the material removing step comprises forming a cutout ( 26A ; 26B ; 26C ; 26D ) in at least one of the rail connecting sections. The method of any one of the preceding claims, wherein the monitoring step comprises coupling the antenna to a radio frequency source, bringing probes ( 42A - 42D ) in juxtaposition with the tracks ( 10A . 10AR - 10D . 10DR ) at predetermined locations, and measuring at least the relative phases of the signals detected by the probes associated with the different respective tracks when the high frequency source is operated. Method according to claim 5, wherein the probes ( 42A - 42D ) are capacitively coupled to the respective tracks. Method according to claim 5 or 6, wherein the probes ( 42A - 42D ) are aligned to path portions corresponding to the positions of voltage minima, the high frequency source being set to the target operating frequency of the antenna. Method according to one of claims 5 to 7, wherein the probes ( 42A - 42D ) are aligned with end portions of the helical tracks. Method according to one of Claims 5 to 8 for producing an antenna in which each track has a first end ( 10AR ; 10BR ; 10CR ; 10DR ) adjacent to a feed point and a second opposite end portion ( 46A ; 46B ; 46C ; 46D ) spaced from the feed location, wherein the material removal step comprises forming cutouts ( 26A - 26D ) in the first end sections and the monitoring step, the positioning of the probes ( 42A - 42D ) in a juxtaposition with the second end portions. Method according to one of the preceding claims, wherein the material is removed from the webs by forming a rectangular opening ( 26A ; 26B ; 26C ; 26D ) in the or each affected web, the opening having a predetermined width transverse to the direction of the web which is automatically calculated in response to the result of the monitoring step. Method according to claim 10, wherein the width and length of the opening ( 26A ; 26B ; 26C ; 26D ) are changeable in response to the monitoring result. The method of any one of the preceding claims, wherein the monitoring step comprises injecting a wobble frequency signal into the antenna over a frequency range including the nominal operating frequency of the antenna, monitoring the relative phases and amplitudes of the signals in the radiating tracks ( 10A ; 10AR - 10D . 10DR ), and the removal of leiti according to material from at least two of the tracks around the frequency at which substantially phase orthogonality occurs closer to the desired operating frequency. The method of any one of claims 1 to 11, wherein the monitoring step includes injecting a wobble frequency signal into the antenna over a frequency range including the nominal operating frequency of the antenna, monitoring the relative phases and amplitudes of signals in the radiating tracks ( 10A . 10AR - 10D . 10DR ) to bring the difference between the monitored phases closer to 90 ° at a central resonance frequency. The method of claim 3, wherein the planar surface has an end surface that is substantially perpendicular to the cylinder axis. 24 ) lies. A helical antenna for circularly polarized radiation at frequencies above 200 MHz, comprising a plurality of substantially helical conductive tracks ( 19A . 10AR - 10D . 10DR ) attached to a dielectric substrate ( 12 ) are arranged, wherein at least one of the tracks a section ( 26A ; 26B ; 26C ; 26D ) of a predetermined size for increasing the inductance of the web. An antenna according to claim 15, wherein the cutout comprises an opening ( 26A ; 26B . 26C . 26D ) disposed between two opposite edges of the web. An antenna according to claim 15 or 16, wherein the substrate ( 12 ) comprises a core formed of a solid dielectric material having a dielectric constant greater than 10, the webs ( 10A . 10AR - 10D ; 10DR ) are arranged so as to define an inner volume of the main part occupied by the solid material of the core, the substrate having curved outer surface portions and flat surface portions which support the webs, and wherein the recesses or any recess ( 26A ; 26B ; 26C ; 26D ) is formed where the respective web lies over a flat surface portion. An antenna according to claim 15 comprising: a substantially cylindrical core ( 12 ) of a dielectric material having a dielectric constant greater than 10, the core having an axis ( 24 ) of the antenna and having a substantially cylindrical outer surface and a pair of end surfaces, the tracks being axially coextensive with outer portions (Figs. 10A - 10D ) on the substantially cylindrical surface and connecting portions ( 10AR - 10DR ) at one of the end surfaces to connect the outer portions to an axial feed point at that end surface, the antenna further comprising an axial feed structure (Figs. 14 ) passing through the core ( 12 ) extends from this one end face to the other end face, and a conductive balun sleeve ( 20 ) which surrounds the core and differs from the feed structure ( 14 ) at the other end face to an edge ( 20U ) located in an axial position between the end faces and connected to the outer track sections, and wherein the cut-out or any cut-out (FIG. 26A ; 26B ; 26C ; 26D ) is in the connecting portion of the respective web or in the outer portion of the respective web at a location adjacent to its connection to the sleeve edge. An antenna according to claim 18, wherein the outer track sections ( 10A - 10D ) comprises two pairs of helical elements, wherein the helical elements of a pair have a different length with respect to the helical elements of the other pair, and wherein each of the tracks of at least one of the pairs has a cutout ( 26A ; 26B ; 26C ; 26D ) having. An antenna according to claim 19, wherein each cutout ( 26A ; 26B ; 26C ; 26D ) an opening of predetermined size in the connecting portion (FIG. 10AR ; 10BR ; 10CR ; 10DR ) of the respective track is.